const byte ledPin = 13;
const byte interruptPin = 2;
volatile byte state = LOW;

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(interruptPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(interruptPin), blink, CHANGE);
 //second LED
  pinMode(12, OUTPUT);
  Serial.begin(9600);
  while (!Serial);

}

void loop() {
  digitalWrite(ledPin, state);
 
}

void blink() {
  state = !state;
 
}